As compared with various display elements, a liquid crystal display element has advantages such as thinner size, light weight, and lower power consumption. The liquid crystal display element is widely used in image display apparatuses such as televisions, videocassette recorders, and the like, and OA (Office Automation) apparatuses such as monitors, word processors, personal computers, and the like.
Conventionally known liquid crystal display methods of the liquid crystal display elements are, for example, the TN (Twisted Nematic) mode in which a nematic liquid crystal is used, display modes in which FLC (Ferroelectric Liquid crystal) or AFLC (Antiferroelectric Liquid crystal) is used, a polymer dispersion type liquid crystal display mode, and a similar mode.
Among the liquid crystal display modes, for example, the TN (Twisted Nematic) mode in which the nematic liquid crystal is used is conventionally adopted in the liquid crystal display elements in practical use. However, the liquid crystal display elements using the TN mode have disadvantages such as slow response, narrow viewing angle, and similar drawbacks. Those disadvantages are large hindrances for the TN mode to take over CRT (Cathode Ray Tube).
Moreover, the display mode in which FLC or AFLC is used has advantages such as high-speed response and wide viewing angles, but is significantly poor in shock-resistant property and temperature property. Therefore, the display mode in which the FLC or AFLC is used has not been widely in practical use.
Further, the polymer dispersion type liquid crystal display mode, which utilizes scattering of light, does not require polarizer and is capable of performing a bright display. However, in principle, the polymer dispersion type liquid crystal display mode cannot control the viewing angle by using a phase plate. Furthermore, the polymer dispersion type liquid crystal display mode has a problem with a response property. Therefore, the polymer dispersion type liquid crystal display mode is not really superior to the TN mode.
In all those display modes, liquid crystal molecules are orientated in a certain direction and thus a displayed image looks different depending on an angle between a line of vision and the liquid crystal molecules. On this account, all those display modes have limits in terms of a viewing angle. Moreover, all those display modes utilize rotation of the liquid crystal molecules which is caused by applying an electric field to the liquid crystal molecules. Because the liquid crystal molecules are rotated in alignment all together, all those display modes take time to respond. Note that, the display modes in which the FLC and the AFLC are used have advantages in the response speed and the viewing angle, but have such a problem that their alignment would be irreversibly destroyed by an external force.
In opposition to those display modes in which the rotation of the molecules by the application of the electric field is utilized, a display mode of an electronic polarization in which the secondary electro-optic effect is utilized is proposed.
The electro-optic effect is a phenomenon in which a refractive index of a material is changed by an external electric field. There are two types of the electro-optic effect: one is an effect proportional to the electric field and the other is proportional to the square of the electric field. The former is called Pockel's effect and the latter is called Kerr effect. Especially Kerr effect (secondary electro-optic effect) has been adopted in high-speed optical shutters early on, and has been practically used in a special measurement instruments. Kerr effect was discovered by J. Kerr in 1875. So far, organic liquid such as nitrobenzene, carbon disulfide, and the like, are known as materials showing Kerr effect. Those materials are used, for example, in the aforementioned optical shutters, and also used for measurement of intensity of high electric fields for power cables and the like.
Later on, it was found that liquid crystal materials have a large Kerr constant. Researches on basic technology have been conducted to utilize the large Kerr constant of the liquid crystal materials for use in optical modulation devices, light deflection devices, and further optical integrated circuit. It was reported that a certain liquid crystal compound has a Kerr constant more than 200 times higher than that of nitrobenzene.
Under those circumstances, studies for utilizing Kerr effect in display apparatuses have been started. Because Kerr effect is proportional to the square of the electric field, it is expected that the utilization of Kerr effect will attain relatively a low voltage driving. Further, it is expected that the utilization of Kerr effect will attain a high-speed response display apparatus because Kerr effect shows a response property of several μ seconds to several m seconds, as its basic nature.
Under those circumstances, for example, Japanese Unexamined Patent Publication No. 249363/2001 (Tokukai 2001-249363, published on Sep. 14, 2001, hereinafter referred to as “Document 1”), Japanese Unexamined Patent Publication No. 183937/1999 (Tokukaihei 11-183937, published on Jul. 9, 1999, hereinafter referred to as “Document 2”, Corresponding U.S. patent application Ser. No. 6,266,109), and “Shiro Matsumoto and three others, “Fine droplets of liquid crystal in a transparent polymer and their response to an electric field”, Appl. Phys., 1996, Lett., 69, p. 1044-1046” (hereinafter referred to as “Non-patent Document 1”) suggest an element to be used as a display element. The element is structured such that a medium made of the liquid crystal material is injected and sealed between a pair of substrates, and an electric field parallel to the substrate or an electric field perpendicular to the substrate is applied to the substrate in order to induce Kerr effect.
Moreover, Document 1 suggests that an alignment treatment should be carried out onto the surface of the substrate in advance so that Kerr effect is easily expressed.
Furthermore, Document 2 suggests that optically-responsive medium should be divided into sub-regions so that Kerr effect is easily expressed.
However, any of the conventional methods cannot adequately reduce the driving voltage for a practical use.